Author Topic: Should the BFR have a launch escape system?  (Read 11829 times)

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 26874
  • Minnesota
  • Liked: 6777
  • Likes Given: 4807
Re: Should the BFR have a launch escape system?
« Reply #100 on: 10/08/2017 10:17 PM »
And yeah, I think it's pretty reasonable for BFR to achieve 99.99% reliability long-term, provided it can get anywhere near the cost figure it's shooting for.

Sure...only 500 times better than F9 with 10 times the complexity.
Yes, because I expect BFR to fly >500x as many times as Falcon 9.

And by reasonable, I meant that it'd be reasonable for the FAA to give that kind of requirement before putting passengers on for point to point.

For spaceflight, the bar should be lower, more like 99.5-99.9%, as that's comparable to a regular rocket (95-99%) with a LAS (catches at most one out of ten rocket failures).
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Oli

  • Senior Member
  • *****
  • Posts: 2103
  • Liked: 374
  • Likes Given: 55
Re: Should the BFR have a launch escape system?
« Reply #101 on: 10/08/2017 10:35 PM »
And yeah, I think it's pretty reasonable for BFR to achieve 99.99% reliability long-term, provided it can get anywhere near the cost figure it's shooting for.

Sure...only 500 times better than F9 with 10 times the complexity.
Yes, because I expect BFR to fly >500x as many times as Falcon 9.

You're talking about ~10k flights per year, how should that happen if BFR doesn't prove to be extremely reliable and cheap beforehand?

« Last Edit: 10/08/2017 10:35 PM by Oli »

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 26874
  • Minnesota
  • Liked: 6777
  • Likes Given: 4807
Re: Should the BFR have a launch escape system?
« Reply #102 on: 10/09/2017 04:49 AM »
And yeah, I think it's pretty reasonable for BFR to achieve 99.99% reliability long-term, provided it can get anywhere near the cost figure it's shooting for.

Sure...only 500 times better than F9 with 10 times the complexity.
Yes, because I expect BFR to fly >500x as many times as Falcon 9.

You're talking about ~10k flights per year, how should that happen if BFR doesn't prove to be extremely reliable and cheap beforehand?
I expect it to do so. More like 1000 per year for many years.


But really: I shouldn't say "expect." What I'm describing is what I think is the best possible outcome that could still happen. I don't really expect it to be that good.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline intrepidpursuit

  • Full Member
  • ****
  • Posts: 429
  • Orlando, FL
  • Liked: 262
  • Likes Given: 182
Re: Should the BFR have a launch escape system?
« Reply #103 on: 10/10/2017 05:20 AM »
There are really two cases here. Risk of LOC (LOP loss of passengers?) on a mission to Mars, a planet 34 million miles away that we could never reach otherwise, and a LOP on a "mission" from LA to Shanghai that could have been done on a plane if you are the type of person who can be patient and kind for 18 hours straight.

For the mission to mars, comparison to Shuttle or upcoming CC vehicles is apt. Shuttle had the main engines attached to the crew compartment, so at the design table traditional abort would have been kind of pointless. It did turn out to lose crew because of its various required appendages and just one close call from its own engines. The BFR will fly many times with the human rated propulsion system before humans ever get on. At least a dozen and maybe 100 launches of the propulsion system before we put people on it. A simple propulsion system (single fuel type, autogenous pressurization, all throttleable and testable engines, no dangly bits) abort modes after the first minute or so of flight, thorough testing, lot of redundancies and engineering led launch team I think can get BFR to Dragon 2 levels of reliability and beyond even without a LES. 1 failure in 370 launches wouldn't put people on that launch.

For a mission to save a business day, the rules are different. Airplanes are scary but are safer than cars. There are hundreds of people on every single flight and it would fly at least hundreds of times a year. The level of safety necessary here is WAY higher. I don't think SpaceX could market this a general transportation until they found some way to make its safety comparable to planes. Whether I would do it or not, regulators would not let a company make money on a system that sacrifices lives for time. Of course, this problem wouldn't actually be solved by a LES, which only helps and does not solve the safety problem.

From a higher level perspective, if a BFS fails after the first few launches, they will probably have a hard time getting buy in. If the operators of the Hindenburg 2 started handing out parachutes for the next flights people still wouldn't get on the thing. This is a spacecraft that will be more valuable than its payloads. It really needs to not blow up; LES or not.

Offline Patchouli

  • Senior Member
  • *****
  • Posts: 4190
  • Liked: 117
  • Likes Given: 208
Re: Should the BFR have a launch escape system?
« Reply #104 on: 10/10/2017 06:09 AM »
Near term BFR probably should have a LAS of sorts though if the spaceship is upgraded to have more then a 1 to 1 thrust to weight ratio without shredding the vacuum engine nozzles and the ability to dump propellant you'd gain much of the benefits of having one except for a scenario where there's a catastrophic failure of the booster on the pad or early in flight.
It might be possible to design the nose of it to be able to detach and survive reentry but this would eat up a lot of mass probably reducing the payload by a third.
I  wonder would having several escape pods based on Dragon's be the way to go on early versions.
As for talks of it flying thousands of times per year and competing directly with airliners I dismiss this as mostly fantasy with the first version of BFR as it's air frame and engines are much higher stressed than an airliner so they will be subject to more wear and tear and need more frequent inspection.

« Last Edit: 10/10/2017 06:44 AM by Patchouli »

Offline JamesH65

  • Full Member
  • ****
  • Posts: 599
  • Liked: 351
  • Likes Given: 8
Re: Should the BFR have a launch escape system?
« Reply #105 on: 10/10/2017 09:57 AM »
Loads of people saying it should have a LAS, but no suggestions on how it could actually be done? Presumably because no-one has yet thought of a way of doing it? Is it even physically possible? All very well saying it should have one, but if having one means the craft never gets made because its either impossible or so hugely expensive, or make the craft useless for its intended purpose, then making it s a requirement is pointless.

Musk has said it won't have one. I guess he may have thought it through.

Offline KelvinZero

  • Senior Member
  • *****
  • Posts: 3468
  • Liked: 453
  • Likes Given: 114
Re: Should the BFR have a launch escape system?
« Reply #106 on: 10/10/2017 10:48 AM »
Loads of people saying it should have a LAS, but no suggestions on how it could actually be done? Presumably because no-one has yet thought of a way of doing it? Is it even physically possible? All very well saying it should have one, but if having one means the craft never gets made because its either impossible or so hugely expensive, or make the craft useless for its intended purpose, then making it s a requirement is pointless.

Musk has said it won't have one. I guess he may have thought it through.
This thread has been specifically separated off from the thread discussing how it could be done, because that was being continually derailed by people posting on the thread who only wanted to say the thread was a dumb idea. :)

http://forum.nasaspaceflight.com/index.php?topic=43923.0

Online guckyfan

  • Senior Member
  • *****
  • Posts: 6311
  • Germany
  • Liked: 1577
  • Likes Given: 1382
Re: Should the BFR have a launch escape system?
« Reply #107 on: 10/10/2017 10:56 AM »
Musk has said it won't have one. I guess he may have thought it through.

I guess he completely goes for reliability of the system. It has to be extremely reliable to work for a very large number of reuses. So he puts engineering for reliablity ahead of a LAS.

I can only think of one reasonable way to have a LAS for the whole crew of 100. Carrying a LAS all the way to Mars is not an option IMO, too much of a weight penalty. So have a separate vehicle, probably a tanker with a capsule on top that crams in 100 people and has its own abort propulsion. That tanker may lose up to 100t of propellant capacity but it would be enough to top off the tanks and bring the passengers. Maybe another launch but launches are cheap. That way the ship can be mostly fueled before passengers arrive.

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 26874
  • Minnesota
  • Liked: 6777
  • Likes Given: 4807
Re: Should the BFR have a launch escape system?
« Reply #108 on: 10/10/2017 11:49 AM »
Seems everyone's assuming a LAS is free.

Giving BFS a LAS would cost billions of dollars and would dramatically reduce the payload in crewed configuration. Better to put those resources to use in improving reliability and a proven flightrate.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline KelvinZero

  • Senior Member
  • *****
  • Posts: 3468
  • Liked: 453
  • Likes Given: 114
Re: Should the BFR have a launch escape system?
« Reply #109 on: 10/10/2017 02:32 PM »
Pulled in from another thread, discussing BFS+Dragon2
In the medium term a Dragon has no place in a BFS architecture. It means carrying a vehicle with plenty of hypergolic propellant. If they want a mobile pod for local actions they would build one based on the BFS RCS-thrusters, maybe a smaller version. It runs on methalox and can be refueled from the BFS main tanks. A Dragon would not be a good match. Such a vehicle needs an airlock. Dragon is designed around the ability to reenter. It has a quite small internal volume due to the cone shape.
I think a dragon, for LAS plus other possible purposes, does have a place in the BFS architecture, in short, medium, and long terms.

Short term:
I think the first BFS produced will be a cargo version. I have heard that the Crew version will be a lot more expensive. Also it may not be allowed near NASA assets for various reasons. I can think of various scenarios where a Dragon on top of and external to a Cargo BFS, instead of continuing with F9, might be considered.

Medium term:
I define medium term as after the Cargo BFS has matured, and the final decisions on the Crew version, based on lessons from the cargo version, must be made. Musk has stated a clear plan for the Crew BFS but I believe that he will prepare for lessons or mistakes from the Cargo BFS to change that plan. He may really want for a Crew version yet not have achieved the safety margins he had hoped for.. yet.

Long term:
Long term I think there is a good reason for a third variant (the debate is simply how significant a variant it must be.. maybe it will end up a trivial modification of the Crew variant. That third variant is *Space Shuttle on steroids variant.* It is quite different from the Crew ( *passengers as cargo* ) variant. Like the shuttle it has a small team actually there to do work and  a large cargo bay with large doors that could take entire satellites on board.

I think a Dragon 2 could give you 100x more safety for many missions, because it is not just a LAS, it duplicates practically everything that you need to survive a trip to space and back. If you think you do not need a 100x more safety, perhaps you should turn that around and ask if you can be doing missions a hundred times more extreme for the same safety.

Asteroid missions could be a good example. Unlike passengers to Mars, you will not have people or even cargo waiting for you. They also do create specific new threats to your heatshield so there is very good reason to want a backup option for that too.

Offline KelvinZero

  • Senior Member
  • *****
  • Posts: 3468
  • Liked: 453
  • Likes Given: 114
Re: Should the BFR have a launch escape system?
« Reply #110 on: 10/10/2017 10:09 PM »
In the medium term a Dragon has no place in a BFS architecture. It means carrying a vehicle with plenty of hypergolic propellant.
Please have that conversation here instead: https://forum.nasaspaceflight.com/index.php?topic=43438.0

...in fact I will quote it there and reply to it there now.

Why there? I am in no way talking about a LES-system but my understanding was that Dragon could become a utility vehicle around BFS. I argued that Dragon is not good for that purpose.
Because you said "In the medium term a Dragon has no place in a BFS architecture. It means carrying a vehicle with plenty of hypergolic propellant."

Therefore your argument is based on dismissing the worth of the BFS having a dragon for a LAS+lifeboat. Obviously the only reason to consider including a heatshield and massive superdraco engines is because these uses are considered as part of the worth of including a crew dragon.

Online guckyfan

  • Senior Member
  • *****
  • Posts: 6311
  • Germany
  • Liked: 1577
  • Likes Given: 1382
Re: Should the BFR have a launch escape system?
« Reply #111 on: 10/11/2017 07:35 AM »
I emphasized that this vehicle is not a LES system but a utility vehicle. My understanding was that this is what was talked about. A Dragon is a poor match for that purpose.

Online Lobo

  • Senior Member
  • *****
  • Posts: 6668
  • Spokane, WA
  • Liked: 516
  • Likes Given: 310
Re: Should the BFR have a launch escape system?
« Reply #112 on: 10/11/2017 11:33 PM »
Musk has said it won't have one. I guess he may have thought it through.

I guess he completely goes for reliability of the system. It has to be extremely reliable to work for a very large number of reuses. So he puts engineering for reliablity ahead of a LAS.

I can only think of one reasonable way to have a LAS for the whole crew of 100. Carrying a LAS all the way to Mars is not an option IMO, too much of a weight penalty. So have a separate vehicle, probably a tanker with a capsule on top that crams in 100 people and has its own abort propulsion. That tanker may lose up to 100t of propellant capacity but it would be enough to top off the tanks and bring the passengers. Maybe another launch but launches are cheap. That way the ship can be mostly fueled before passengers arrive.

Back when I was working with the design team that was working on concepts of what the Mars Transportation System might look like, before Musk unveiled the ITS system a year ago, the issue of an LAS was debated.  We eventually came up with a biconic design as well as a Super Dragon Capsule type of design that sat on a reusable 2nd stage.
The Super Dragon Capsule design was easier to put an LAS on, as it sat on a 2nd stage and was launch unfueled.  So it only had enough propellant for abort, and then would be refueled in orbit.  But it had other drawbacks like door in the heat shield for the engines, as well as both pressure fed fast fire abort engines and pump fed normal propulsion engines.  And it was 3 pieces instead of just 2 like the biconic concept.

I'd always favored a 2-piece biconic design overall for simplicity and capability, and eventually I won out with that in the team.  But the rest of the team still thought it would have an LAS, so we worked one into it.  But I still never thought SpaceX's design would have one.  And that has turned out to be correct. 
The main reasons are there's a lot of design compromises.  The ship is already going to be very complex without introducing more failure modes and complexity into it.  While an LAS would help with launch, it becomes a liability in cost and capacity, and even an extra point of failure after that, with no real benefits.

The way I saw it, early on, the crews would be small.  Probably no more than 7, which Dragon 2 could take up as it would already be flying and available to do so, and it has an LAS.  If you wanted 14, you could do two Dragon 2 launches for the crew.  With reusable boosters and spacecraft, that's really not that prohibitive.  After that, BFR should have established a flight track record.  As it would have redundant engines, and tolerate an engine out at any point during launch, that really reduces the failure modes for a liquid rocket.  There could still be a complete explosion on the pad or lift off, which would result in the loss of crew, but barring that, it should be able to tolerate most other issues with a safe abort mode.

But even so, if the customer still demand an LAS system, a modified ship could be built that would have an LAS, and be used as a crew taxi to take a full crew of 100 up just before departure from orbit.  It would sacrifice it's payload for that LAS system but it would be just a reusable crew taxi, and that would be it's only job.  If an LAS was a must, then that was the way to do it rather than to try to integrate it into the interplanetary ship.  It'll already have enough jobs that it must do.
But...it will be a long time before the crews would be anywhere near that big.  You need to have a lot of infrastructure on the Moon or Mars to support adding 100 new people on a single mission, so that's a long time down the road, and Falcon/Dragon can handle the smaller crews in the mean time.





Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 26874
  • Minnesota
  • Liked: 6777
  • Likes Given: 4807
Re: Should the BFR have a launch escape system?
« Reply #113 on: 10/12/2017 01:44 PM »
By the way, a LAS would add its own risk factors. For instance, if the LAS on Orion fails to separate, the crew dies.
And commercial airlines are so safe that if you added a LAS or ejection seats to them, the extra risks would greatly outweigh the abort advantages, and you'd REDUCE overall safety.

Again, for those in the back:
If BFR is as reliable as Musk wants it to be, adding a LAS would REDUCE safety.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline AncientU

  • Senior Member
  • *****
  • Posts: 4685
  • Liked: 2806
  • Likes Given: 3925
Re: Should the BFR have a launch escape system?
« Reply #114 on: 10/12/2017 04:26 PM »
I can't believe that someone is building a NOVA-class, fully reusable launcher and all this focus on a friggin' launch escape system.
Get over it...
« Last Edit: 10/12/2017 04:27 PM by AncientU »
"If we shared everything [we are working on] people would think we are insane!"
-- SpaceX friend of mlindner

Offline Semmel

  • Full Member
  • ****
  • Posts: 1080
  • Germany
  • Liked: 768
  • Likes Given: 2217
Re: Should the BFR have a launch escape system?
« Reply #115 on: 10/12/2017 04:47 PM »
Robotbeat, I agree with you. However the question is not based purely on statistics but also on human nature. If you have a LOC event, it's a big difference in public opinion if it reads "despite the LAS, the failure was so severe that no one survived." or "no one survived and the rocket didn't even have an ejection seat.". At this point it does not matter if a LAS would have caused the failure and didn't save the crew. In the mind of the public, a LAS makes you seem to try harder even if the engineering said otherwise. As an engineer, it huts me to say this but here are some examples..

In the US, many more people are scared of terrorism than car crashes, despite the fact that it is far more likely to die in a car than by a terrorist attack. And there are no anti car laws put in place. Jet we see legislation after legislation giving advanced rights to the police to counter the terrorist threat. That is just an example of how nonsensical public perception can be. And the same will happen to a BFR with or without a LAS. This can mean life and death of SpaceX.

Also, I am not arguing in favor of a LAS here. I share your concern that a LAS can make BFR less safe. But I want to point out that we can't restrict the discussion on the engineering aspects.

Online Norm38

  • Full Member
  • ****
  • Posts: 968
  • Liked: 368
  • Likes Given: 492
Re: Should the BFR have a launch escape system?
« Reply #116 on: 10/12/2017 06:49 PM »
A big difference in human nature deals with private vs. public spending.  When astronauts are government employees and national heroes and they are killed in an accident, every citizen feels they are a stakeholder, that it was their money being spent, and why oh why wasn't more done.

Change that over to the same number of people killed while flying an experimental aircraft on their dime, and the public shrugs it off. People are allowed to risk their lives with their money.
We need to get to commercial operations where people who accept the risks are buying their own tickets.  At that point governments will put their crew on it, just like government employees fly commercial and don't all fly in military transports strapped into ejection seats.

Airliners like TWA 800 have exploded with great loss of life, far more than 14 people.  And no one asked why 747s don't have escape capsules, and Boeing hasn't redesigned the 747 to add them.  Passengers still fly, because there's no other way to get to their destination. If people want to go to Mars, they will accept the risks that come with the trip.

The only way that we are going to get to airliner level operations and reliability is to simply just do it that way.

Offline Semmel

  • Full Member
  • ****
  • Posts: 1080
  • Germany
  • Liked: 768
  • Likes Given: 2217
Re: Should the BFR have a launch escape system?
« Reply #117 on: 10/12/2017 07:11 PM »
I dont want to defend how the public opinion often works. I find it quite nonsensical my self. But look how the reaction was to the first Tesla autopilot death. It got way more attention than it should have. Way more than any other car accident got. Now imagine this wasnt a self driving car with a guy not paying attention where he should have, but maybe one of the first BFR point to point flights. I dont think my self that accidents should be a deciding factor. But public opinion should at least go into the equation. I agree, it should not dominate it.

Offline KelvinZero

  • Senior Member
  • *****
  • Posts: 3468
  • Liked: 453
  • Likes Given: 114
Re: Should the BFR have a launch escape system?
« Reply #118 on: 10/12/2017 10:02 PM »
By the way, a LAS would add its own risk factors. For instance, if the LAS on Orion fails to separate, the crew dies.
And commercial airlines are so safe that if you added a LAS or ejection seats to them, the extra risks would greatly outweigh the abort advantages, and you'd REDUCE overall safety.

Again, for those in the back:
If BFR is as reliable as Musk wants it to be, adding a LAS would REDUCE safety.
Do you have a reference for that? I assumed it was cost, but I can imagine it being true.

Offline yg1968

  • Senior Member
  • *****
  • Posts: 9066
  • Liked: 1113
  • Likes Given: 755
Re: Should the ITS have a launch escape system?
« Reply #119 on: 10/12/2017 11:47 PM »
Its LES is pretty much the engines on the bottom of the ship, you can't have an escape system that large.

It's similar to the crewed Dream Chaser's abort system.
« Last Edit: 10/12/2017 11:53 PM by yg1968 »

Tags: